The invention is directed to an oil return apparatus for a refrigeration system and more particularly to an oil return apparatus which is placed in a return line at the lowest point of the piping between an evaporator and a compressor which prevents oil collection in the evaporator while trapping and returning the oil to the compressor. The apparatus must be placed as close as possible to the evaporator.
The device of this invention may be placed in the suction or return line of a refrigeration system to replace well known traps such as a U-bend in a pipe or other arrangements, one such device being set forth in U.S. Pat. No. 3,257,824.
It is well known in the art that refrigeration systems operating at full capacity have little problems with oil return to the compressor. However, when the compressor is operating at very low capacities, the entrained or occluded lubricant tends to become separated from the gaseous refrigerant settling at low points or at the bottom of riser elements in the system. If the oil settles at risers there is a danger that insufficient oil is returned to the compressor or that gulps of oil will be returned which may damage the compressor. It is therefore desirable that the system be kept free of oil collection areas and that the oil be returned constantly to the compressor without any great buildup at any oil collection areas.
It is well known that in supermarkets as well as other places, the cooling evaporators are from 25 feet to 125 feet from the compressor; therefore, it is very important that the pressure drop be kept at a minimum. For every 90.degree. elbow installed in the suction line, the pressure drop is estimated to be equal to two feet of pipe. Further, supermarket freezers are maintained at about minus 20.degree. using F-502 refrigerant. The back pressure at about minus 20.degree. F. is from 2 to 3 lbs depending upon the length of the pipe. Since temperature equals pressure and the lower the temperature, the lower the pressure. At this pressure, the velocity through any lubricant entrained part must be sufficient to carry the entrained lubricant through the piping to the compressor.
It is therefore an object of the invention to provide a device which will return the lubricant of the system to the compressor without any buildup of lubricant in the device.
Another object of the invention is to provide a device which functions to return lubricant to a compressor without any entrainment of lubricant even at low operating pressure.